Anything that changes your gait on a long run is going to have a big impact, and carrying water is probably the most common culprit. So here’s the key to doing it right.
Do It Symmetrically
Handheld water bottles are pretty popular because they’re simple and inexpensive and it’s really easy to take a drink. But adding weight to one side of your body imbalances your whole body, moving your weight onto the opposite leg and keeping it there. This can cause injuries, especially plantar fascia problems and IT band syndrome.
Furthermore, not only have you added weight to only one side of your body, you’ve also added it at the end of a pendulum–your arm–where it will have the biggest effect. And it’s sloshing in the bottle, creating a force that even further works your arm, shoulder and back muscles on that side, increasing the asymmetry of your gait and stressing the opposite leg even further.
Sometimes people opt for switching the bottle from one hand to the other every km or so, which is an option, but you’re still going to be working harder with one side of your body or the other for the whole run, which robs you of energy you could be putting into simply covering ground.
So I recommend you do not use a handheld bottle.
Do It Close to the Center of Your Body
The center of your body–your torso–will be least impacted by the addition of a bit of weight. So a hydration belt, with several bottles you can arrange around your waist, is a good option. But a hydration pack–a backpack-style water bladder with a tube you drink from–is an even better one because adding weight a little bit higher up can help you run a little bit faster.
Keep Your Armswing and Core Action Normal
It’s critical that your belt or pack allows you to swing your arms exactly the same as you normally would, as well as allowing your pelvis and upper body to move normally in what I call the core action. So you may have to try a few different options in a running store to find one that suits you.
These three simple criteria will definitely help your performance on long runs, allow you to hydrate, and keep your gait balanced. For a bit more detail and demonstration, here’s my YouTube video on the topic: